actually that’s 100% wrong, it is in the CBA, yet here you are still crying about it.
The practice, optional or not, is a violation of Article 16.5(b) of the Collective Bargaining Agreement between the NHL and the NHLPA. The section reads as follows:
(b) December 24, Christmas Day and December 26 shall be off-days for all purposes, including travel, and no Club may request a Player's consent to practice on such days for any reason, provided, however, if December 26 falls on a Saturday and the League has scheduled NHL Games on such date, December 23 may be substituted as an off-day for all purposes, including travel, instead of December 26.